'\" te
.\" This manual page is derived from the DAT/uDAPL 1.2 specification.
.\" Portions Copyright (c) 2007, Sun Microsystems, Inc. All Rights Reserved.
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.TH DAT_SRQ_CREATE 3DAT "Sep 11, 2006"
.SH NAME
dat_srq_create \- create an instance of a shared receive queue
.SH SYNOPSIS
.LP
.nf
cc [ \fIflag\fR\&.\|.\|. ] \fIfile\fR\&.\|.\|. \fB-ldat\fR [ \fIlibrary\fR\&.\|.\|. ]
#include <\fBdat/udat.h\fR>

DAT_RETURN
    dat_srq_create (
        IN      DAT_IA_HANDLE       ia_handle,
        IN      DAT_PZ_HANDLE       pz_handle,
        IN      DAT_SRQ_ATTR        *srq_attr,
        OUT     DAT_SRQ_HANDLE      *srq_handle
    )
.fi

.SH PARAMETERS
.sp
.ne 2
.na
\fB\fIia_handle\fR\fR
.ad
.RS 14n
A handle for an open instance of the IA to which the created SRQ belongs.
.RE

.sp
.ne 2
.na
\fB\fIpz_handle\fR\fR
.ad
.RS 14n
A handle for an instance of the Protection Zone.
.RE

.sp
.ne 2
.na
\fB\fIsrq_attr\fR\fR
.ad
.RS 14n
A pointer to a structure that contains Consumer-requested SRQ attributes.
.RE

.sp
.ne 2
.na
\fB\fIsrq_handle\fR\fR
.ad
.RS 14n
A handle for the created instance of a Shared Receive Queue.
.RE

.SH DESCRIPTION
.sp
.LP
The \fBdat_srq_create()\fR function creates an instance of a Shared Receive
Queue (SRQ) that is provided to the Consumer as \fIsrq_handle\fR. If the value
of \fBDAT_RETURN\fR is not \fBDAT_SUCCESS\fR, the value of \fIsrq_handle\fR is
not defined.
.sp
.LP
The created SRQ is unattached to any Endpoints.
.sp
.LP
The Protection Zone \fIpz_handle\fR allows Consumers to control what local
memory can be used for the Recv DTO buffers posted to the SRQ. Only memory
referred to by LMRs of the posted Recv buffers that match the SRQ Protection
Zone can be accessed by the SRQ.
.sp
.LP
The \fIsrq_attributes\fR argument specifies the initial attributes of the
created SRQ. If the operation is successful, the created SRQ will have the
queue size at least \fImax_recv_dtos\fR and the number of entries on the posted
Recv scatter list of at lease \fImax_recv_iov\fR. The created SRQ can have the
queue size and support number of entries on post Recv buffers larger than
requested. Consumer can query SRQ to find out the actual supported queue size
and maximum Recv IOV.
.sp
.LP
The Consumer must set \fIlow_watermark\fR to \fBDAT_SRQ_LW_DEFAULT\fR to ensure
that an asynchronous event will not be generated immediately, since there are
no buffers in the created SRQ. The Consumer should set the Maximum Receive DTO
attribute and the Maximum number of elements in IOV for posted buffers as
needed.
.sp
.LP
When an associated EP tries to get a buffer from SRQ and there are no buffers
available, the behavior of the EP is the same as when there are no buffers on
the EP Recv Work Queue.
.SH RETURN VALUES
.sp
.ne 2
.na
\fB\fBDAT_SUCCESS\fR\fR
.ad
.RS 30n
The operation was successful.
.RE

.sp
.ne 2
.na
\fB\fBDAT_INSUFFICIENT_RESOURCES\fR\fR
.ad
.RS 30n
The operation failed due to resource limitations.
.RE

.sp
.ne 2
.na
\fB\fBDAT_INVALID_HANDLE\fR\fR
.ad
.RS 30n
Either \fIia_handle\fR or \fIpz_handle\fR is an invalid DAT handle.
.RE

.sp
.ne 2
.na
\fB\fBDAT_INVALID_PARAMETER\fR\fR
.ad
.RS 30n
One of the parameters is invalid. Either one of the requested SRQ attributes
was invalid or a combination of attributes is invalid.
.RE

.sp
.ne 2
.na
\fB\fBDAT_MODEL_NOT_SUPPORTED\fR\fR
.ad
.RS 30n
The requested Model was not supported by the Provider.
.RE

.SH USAGE
.sp
.LP
SRQ is created by the Consumer prior to creation of the EPs that will be using
it.  Some Providers might restrict whether multiple EPs that share a SRQ can
have different Protection Zones. Check the \fIsrq_ep_pz_difference_support\fR
Provider attribute. The EPs that use SRQ might or might not use the same
\fIrecv_evd\fR.
.sp
.LP
Since a Recv buffer of SRQ can be used by any EP that is using SRQ, the
Consumer should ensure that the posted Recv buffers are large enough to receive
an incoming message on any of the EPs.
.sp
.LP
If Consumers do not want to receive an asynchronous event when the number of
buffers in SRQ falls below the Low Watermark, they should leave its value as
\fBDAT_SRQ_LW_DEFAULT\fR. If Consumers do want to receive a notification, they
can set the value to the desired one by calling \fBdat_srq_set_lw\fR(3DAT).
.sp
.LP
SRQ allows the Consumer to use fewer Recv buffers then posting the maximum
number of buffers for each connection. If the Consumer can upper bound the
number of incoming messages over all connections whose local EP is using SRQ,
then instead of posting this maximum for each connection the Consumer can post
them for all connections on SRQ. For example, the maximum utilized link
bandwidth divided over the message size can be used for an upper bound.
.sp
.LP
Depending on the underlying Transport, one or more messages can arrive
simultaneously on an EP that is using SRQ. Thus, the same EP can have multiple
Recv buffers in its possession without these buffers being on SRQ or
\fIrecv_evd\fR.
.sp
.LP
Since Recv buffers can be used by multiple connections of the local EPs that
are using SRQ, the completion order of the Recv buffers is no longer guaranteed
even when they use of the same \fIrecv_evd\fR. For each connection the Recv
buffers completion order is guaranteed to be in the order of the posted
matching Sends to the other end of the connection.  There is no ordering
guarantee that Receive buffers will be returned in the order they were posted
even if there is only a single connection (Endpoint) associated with the SRQ.
There is no ordering guarantee between different connections or between
different \fIrecv_evd\fRs.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard: uDAPL, 1.2
_
MT-Level	Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR dat_srq_free (3DAT),
.BR dat_srq_post_recv (3DAT),
.BR dat_srq_query (3DAT),
.BR dat_srq_resize (3DAT),
.BR dat_srq_set_lw (3DAT),
.BR libdat (3LIB),
.BR attributes (7)
